1. Field of the Invention
The field of the invention generally relates to medical devices for treating disorders of the skeletal system.
2. Description of the Related Art
Distraction osteogenesis is a technique which has been used to grow new bone in patients with a variety of defects. For example, limb lengthening is a technique in which the length of a bone (for example a femur or tibia) may be increased. By creating a corticotomy, or osteotomy, in the bone, which is a cut through the bone, the two resulting sections of bone may be moved apart at a particular rate, such as one (1.0) mm per day, allowing new bone to regenerate between the two sections as they move apart. This technique of limb lengthening is used in cases where one limb is longer than the other, such as in a patient whose prior bone break did not heal correctly, or in a patient whose growth plate was diseased or damaged prior to maturity. In some patients, stature lengthening is desired, and is achieved by lengthening both femurs and/or both tibia to increase the patient's height.
Bone transport is a similar procedure, in that it makes use of osteogenesis, but instead of increasing the distance between the ends of a bone, bone transport fills in missing bone in between. There are several reasons why significant amounts of bone may be missing. For example, a prior non-union of bone, such as that from a fracture, may have become infected, and the infected section may need to be removed. Segmental defects may be present, the defects often occurring from severe trauma when large portions of bone are severely damaged. Other types of bone infections or osteosarcoma may be other reasons for a large piece of bone that must be removed or is missing.
Limb lengthening is often performed using external fixation, wherein an external distraction frame is attached to the two sections of bone by pins which pass through the skin. The pins can be sites for infection and are often painful for the patient, as the pin placement site remains a somewhat open wound “pin tract” throughout the treatment process. The external fixation frames are also bulky, making it difficult for patient to comfortably sit, sleep and move. Intramedullary lengthening devices also exist, such as those described in U.S. Patent Application Publication No. 2011/0060336, which is incorporated by reference herein. Bone transport is typically performed by either external fixation, or by bone grafting.
In external fixation bone transport, a bone segment is cut from one of the two remaining sections of bone and is moved by the external fixation, usually at a rate close to one (1.0) mm per day, until the resulting regenerate bone fills the defect. The wounds created from the pin tracts are an even worse problem than in external fixation limb lengthening, as the pins begin to open the wounds larger as the pins are moved with respect to the skin. In bone grafting, autograft (from the patient) or allograft (from another person) is typically used to create a lattice for new bone growth. Bone grafting can be a more complicated and expensive surgery than the placement of external fixation pins.